How can i active again a render texture after set it to null ?

I have two cameras in the hierarchy. "Camera" is displaying when running the game using render texture raw image and canvas in the game view bottom right corner.

When i click on C key to switch the cameras between Main Camera and Camera i set the render textire active and the Camera render texture to null:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class SwitchCameras : MonoBehaviour {
 
     public Camera[] cameras;
     public int currentCamera = 0;
     public GameObject objectToHide;
     public RenderTexture rt;
 
     void Awake()
     {
         if (cameras == null || cameras.Length == 0)
         {
             Debug.LogError("No cameras assigned..", gameObject);
             this.enabled = false;
         }
     }
 
     void Update()
     {
         if (Input.GetKeyDown(KeyCode.C))
         {
             // disable current
             cameras[currentCamera].enabled = false;
 
             // increment index and wrap after finished array
             currentCamera = (currentCamera + 1) % cameras.Length;
 
             // enable next
             cameras[currentCamera].enabled = true;
 
             if (cameras[currentCamera].name == "Camera")
             {
                 objectToHide.GetComponent<Renderer>().enabled = false;
                 RenderTexture.active = null;
                 cameras[currentCamera].targetTexture = null;
             }
             else
             {
                 objectToHide.GetComponent<Renderer>().enabled = true;
                 RenderTexture.active = rt;
                 for (int i = 0; i < cameras.Length; i++)
                 {
                     if (cameras[i].name == "Camera")
                         cameras[i].targetTexture = rt;
                 }
             }
         }
     }
 
     void EnableOnlyFirstCamera()
     {
         for (int i = 0; i < cameras.Length; i++)
         {
             // only 1==0 returns true
             cameras[i].enabled = (i == 0);
         }
     }
 }
 

This is the two lines i set the render text to null:

  RenderTexture.active = null;
 cameras[currentCamera].targetTexture = null;

What it does is freezing the Camera picture to still in the bottom right corner. Then when switching back to the Main Camera i'm trying to active the Camera again:

 RenderTexture.active = rt;
                     for (int i = 0; i < cameras.Length; i++)
                     {
                         if (cameras[i].name == "Camera")
                             cameras[i].targetTexture = rt;
                     }

But the Camera not active there is still a frozen image inside like the render texture is not active.